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ECG Findings

  • Sinus tachycardia, nonspecific ST-T changes.

  • Precordial T-wave inversions.

  • Prominent S wave in lead I, Q wave in lead III, and inverted T wave in III (S1/Q3/T3).

  • Incomplete or complete RBBB, P pulmonale (lead II).

  • Rightward axis.

  • ST-segment elevation (especially in leads V1, aVR) and ST-segment depression may occur in cases of large pulmonary emboli.


  1. No ECG pattern is diagnostic for pulmonary embolism. Small-to-moderate emboli may not affect the ECG.

  2. With large emboli, increased resistance to pulmonary arterial flow produces right ventricle overload and dilation.

  3. Increased right atrial pressures may produce P pulmonale (tall P waves > 2.5 mm in lead II) or atrial dysrhythmias.


Sinus Tachycardia and S1Q3T3 Pattern in a Patient with Acute Pulmonary Embolism. (ECG contributor: James V. Ritchie, MD.)


S wave is apparent in lead I (blue arrowhead), Q wave in lead III (black arrowhead), and inverted T wave in lead III (blue arrow).

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